This invention relates generally to measuring driving forces, and more particularly to a fixture for measuring the driving forces imparted to a sheet by a friction sheet feeding apparatus.
Certain typical mechanisms for feeding sheets in common use today employ friction driving forces to transport the sheets. For example, to improve productivity of modern high speed reproduction equipment, such as copier/duplicators, mechanisms have been provided for friction feeding original document sheets to the exposure platen. One such original document sheet feeder is shown in U.S. Application Ser. No. 647,683, filed Jan. 8, 1976, in the name of Matthew J. Russel. This feeder sequentially removes original document sheets from a supply stack, delivers the sheets seriatim to a registration position on the exposure platen, and returns the sheets to the stack after images thereof have been recorded. Feeding of the sheets across the platen is by a plurality of rotating friction rollers imparting driving forces to the sheets. Of course, feeding could be accomplished by other types of friction drives such as moving belts.
While friction feeding of original document sheets has proven to be generally successful in delivering sheets to the registration position on the exposure platen, accurate adjustment of the friction feed is required to insure proper transport of the sheets. Specifically, if the friction driving forces imparted to the document sheets are not high enough, the feeder may slip relative to the sheets and the sheets will not reach the registration position; and if the friction driving forces are to high, the sheets may be damaged, or may develop a sufficiently high triboelectric charge as they move across the platen so as to become tacked to the platen thus inteferring with the feeding action. Although coarse adjustment of the friction driving forces of the feeder is provided by particular selection of the material of the friction drive and its general location relative to a sheet being fed, fine tuning of the forces is typically accomplished by trial-and-error adjustment of the specific location of the friction drive to change the normal force of the sheets. Such trial-and-error adjustment has not proven highly satisfactory when particularly accurate feeding forces are desired.
Various apparatus are known for measuring friction driving forces of rotating members (see, for example, U.S. Pat. Nos. 1,775,076 and 1,831,198). However, such apparatus have not been found suitable for measuring the driving forces of document sheet feeders of the above described type. This is due to the minimal space available when the feeder is operatively positioned over the exposure platen and the inability of such apparatus to accurately duplicate the operative function of the friction drive so as to give a true picture of the driving force action during normal operation.